Zoom lens and imaging apparatus

ABSTRACT

A zoom lens substantially consists of, in order from the object side, a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a negative fifth lens group. When varying magnification, the distances between adjacent lens groups) are changed, while all of the lens groups are moved with respect to an image formation position. When focusing, only the fifth lens group is shifted, and the third lens group has a third-a lens group having positive refractive power and a third-b lens group having negative refractive power, which are arranged in this order from the object side, only the third-b lens group is moved in a direction perpendicular to the optical axis to achieve camera shake correction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens having a high variablemagnification ratio used in electronic cameras such as digital cameras,video cameras, broadcasting cameras, surveillance cameras and the like,to a zoom lens having a camera shake correction function, and to animaging apparatus including the zoom lens.

2. Description of the Related Art

Conventionally, a zoom lens substantially consisting of: a first lensgroup having positive refractive power; a second lens group havingnegative refractive power; a third lens group having positive refractivepower; a fourth lens group having positive refractive power; and a fifthlens group having negative refractive power, which are arranged in thisorder from the object side, is known as a zoom lens having relatively ahigh variable magnification ratio. The zoom lens with such a lensconstruction is known to be appropriate for realizing both a highvariable magnification ratio and a reduction in size (see JapaneseUnexamined Patent Publication No. 4 (1992)-070707, U.S. Pat. No.5,872,659, and Japanese Unexamined Patent Publication No. 11(1999)-064728)

As a zoom lens having “a camera shake correction function (avibration-proof function)” for preventing image blurring attributed tovibration, camera shake and the like, a zoom lens that substantiallyconsists of a first lens group having positive refractive power, asecond lens group having negative refractive power, a third lens grouphaving positive refractive power, and a fourth lens group havingpositive refractive power, arranged in this order from the object side,the third lens group of which comprises two groups, a partial grouphaving positive refractive power and a partial group having negativerefractive power, and that exhibits camera shake correction effects bymoving the partial group having negative refractive power in a directionperpendicular to an optical axis, is known (see U.S. Pat. No. 6,462,885)

SUMMARY OF THE INVENTION

Recently, there is demand for a zoom lens, which has a camera shakecorrection function and is compact, and yet has a high variablemagnification ratio, e.g., a zoom lens which has a high variablemagnification ratio of over 12×, and yet which is compact and capable ofhigh performance.

However, conventionally known compact and high performance zoom lenses,e.g., the zoom lenses disclosed in see Japanese Unexamined PatentPublication No. 4 (1992)-070707, U.S. Pat. No. 5,872,659, and JapaneseUnexamined Patent Publication No. 11 (1999)-064728, have variablemagnification ratios of less than 10×, and cannot necessarily be said tohave high variable magnification ratios.

The present invention has been developed in view of the foregoingcircumstances. It is an object of the present invention to provide azoom lens, which has a high variable magnification ratio, and yet whichis compact, capable of high performance, and has a camera shakecorrection function, as well as an imaging apparatus including the zoomlens.

A zoom lens of the present invention substantially consists of:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power;

a fourth lens group having positive refractive power; and

a fifth lens group having negative refractive power, which are arrangedin this order from an object side,

wherein when varying magnification from a wide angle end to a telephotoend, the distance between the first lens group and the second lens groupis consistently increased, the distance between the second lens groupand the third lens group is consistently decreased, the distance betweenthe third lens group and the fourth lens group is consistentlydecreased, and the distance between the fourth lens group and the fifthlens group is changed, while all of the lens groups are moved withrespect to an image formation position,

wherein when moving a point of focus from an infinity side to a nearside to achieve focus, only the fifth lens group is moved from theobject side to the image side,

the third lens group comprises a third-a lens group having positiverefractive power and a third-b lens group having negative refractivegroup, which are arranged in this order from the object side, and

only the third-b lens group is moved in a direction perpendicular to theoptical axis to achieve camera shake correction.

The zoom lens may substantially consist of five lens groups. In thiscase, the expression “zoom lens which substantially consists of n lensgroups” refers to a zoom lens that includes lenses substantially withoutany refractive power; optical elements other than lenses such asapertures and glass covers; and mechanical components such as lensflanges, lens barrels, imaging elements, and camera shake correctionmechanisms; in addition to the n lens groups.

Further, it is desirable for the zoom lens 100 to satisfy formula (M):−2.00<f_(3a)/f_(3b)<−0.85, and more desirably, formula (M′):−1.00<f_(3a)/f_(3b)<−0.85, where f_(3a) is the focal length of thethird-a lens group 3Ga, and f_(3b) is the focal length of the third-blens group 3Gb.

The third-b lens group 3Gb may substantially consist of one negativelens and one positive lens.

The third-b lens group 3Gb can be composed of two single lenses and atleast one surface can be an aspheric lens.

An imaging apparatus of the present invention is equipped with the zoomlens of the present invention.

The zoom lens and the imaging apparatus including the zoom lensaccording to the present invention substantially consist of:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power;

a fourth lens group having positive refractive power; and

a fifth lens group having negative refractive power, which are arrangedin this order from the object side of the zoom lens,

wherein when varying magnification from a wide angle end to a telephotoend, the distance between the first lens group and the second lens groupis consistently increased, the distance between the second lens groupand the third lens group is consistently decreased, the distance betweenthe third lens group and the fourth lens group is consistentlydecreased, and the distance between the fourth lens group and the fifthlens group is changed such that all of the lens groups moved withrespect to an image formation position,

wherein when moving a point of focus from an infinity side to a nearside to achieve focus, only the fifth lens group is moved from theobject side to the image side,

wherein the third lens group comprises a third-a lens group havingpositive refractive power and a third-b lens group having negativerefractive power, which are arranged in this order from the object side,and

only the third-b lens group is moved in a direction perpendicular to theoptical axis so as to achieve camera shake correction, thereby enablingthe zoom lens to have a high variable magnification ratio, and yet to becompact, be capable of high performance and have a camera shakecorrection function.

Thus, for example, a zoom lens which has a full angle of view at a wideangle end exceeding 75°, that is, a large angle of view, and whichfurther has a high variable magnification ratio exceeding 12×, and yetis compact, capable of high performance, and has a camera shakecorrection function, can be configured.

More specifically, the zoom lens of the present invention configured asdescribed above can facilitate suppression of performance variations inthe zoom intermediate range, compared to conventionally known zoomlenses (a zoom lens that is constituted of four lens groups: a firstlens group having positive refractive power, a second lens group havingnegative refractive power, a third lens group having positive refractivepower, and a fourth lens group having negative refractive power, whichare arranged in this order from the object side).

Further, when changing focusing positions from the infinity side towardthe near side, only the fifth lens group is moved from the object sideto the image side. This enables a reduction in size and weight of thefocusing group (the fifth lens group 5G), thereby reducing the burden ona focus mechanism, and realizing high-speed focus.

Further, the camera shake correction can be carried out by moving onlythe third-b lens group that constitutes the third lens group in adirection perpendicular to the optical axis, which enables reducing adiameter of luminous flux by positive refractive power of the third-alens group before transmitting this luminous flux through the third-blens group. Thereby, the effective diameter of the third-b lens groupcan be small, which can reduce a weight of a camera shake correctiongroup (the third-b lens group). This can realize a reduction in theburden on the camera shake correction mechanism for enabling themovement of the third-b lens group in a direction perpendicular to theoptical axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional diagram illustrating the structureof a zoom lens and an imaging apparatus including the zoom lensaccording to an embodiment of the present invention;

FIG. 2A is a cross sectional diagram illustrating a zoom lens of Example1;

FIG. 2B is a cross sectional diagram illustrating each of a case that azoom setting of the zoom lens of Example 1 is set to a wide angle endand a case that a zoom setting thereof is set to a telephoto end;

FIG. 3A is a cross sectional diagram illustrating a zoom lens of Example2;

FIG. 3B is a cross sectional diagram illustrating each of a case that azoom setting of the zoom lens of Example 2 is set to the wide angle endand a case that a zoom setting thereof is set to the telephoto end;

FIG. 4A is a cross sectional diagram illustrating a zoom lens of Example3;

FIG. 4B is a cross sectional diagram illustrating each of a case that azoom setting of the zoom lens of Example 3 is set to the wide angle endand a case that a zoom setting thereof is set to the telephoto end;

FIG. 5A is a cross sectional diagram illustrating a zoom lens of Example4;

FIG. 5B is a cross sectional diagram illustrating each of a case that azoom setting of the zoom lens of Example 4 is set to the wide angle endand a case that a zoom setting thereof is set to the telephoto end;

FIG. 6A is a cross sectional diagram illustrating a zoom lens of Example5;

FIG. 6B is a cross sectional diagram illustrating each of a case that azoom setting of the zoom lens of Example 5 is set to the wide angle endand a case that a zoom setting thereof is set to the telephoto end;

FIG. 7 is an aberration diagram of Example 1;

FIG. 8 is an aberration diagram of Example 2;

FIG. 9 is an aberration diagram of Example 3;

FIG. 10 is an aberration diagram of Example 4; and

FIG. 11 is an aberration diagram of Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the zoom lens ad the imaging apparatus including the lensof the present invention will be described with reference to theattached drawings.

FIG. 1 is a schematic cross sectional diagram illustrating the structureof a zoom lens and an imaging apparatus including the zoom lensaccording to an embodiment of the present invention.

The zoom lens 100 as shown in the Figure has a high variablemagnification ratio, and yet is compact, capable of high performance,and has a camera shake correction function. The imaging apparatus 200equipped with the zoom lens 100 is used as a digital still camera, avideo camera, a surveillance camera, or the like.

The zoom lens 100 comprises a first lens group 1G having positiverefractive power, a second lens group 2G having negative refractivepower, a third lens group 3G having positive refractive power, a fourthlens group 4G having positive refractive power, and a fifth lens group5G having negative refractive power, in this order from an object side(the side of −Z in the Figures).

The zoom lens 100 consistently increases a distance 612 between thefirst lens group 1G and the second lens group 2G, consistently decreasesa distance 623 between the second lens group 2G and the third lens group3G, consistently decreases a distance 634 between the third lens group3G and the fourth lens group 4G, and changes a distance 645 between thefourth lens group 4G and the fifth lens group 5G, while all of the lensgroups 1G through 5G are moved with respect to an image formationsurface Mk which is an image formation position of the zoom lens 100,when zooming from the wide angle end to the telephoto end (continuouslyvarying magnification).

Further, the above zoom lens 100 is designed to move only the fifth lensgroup 5G to the image side to achieve focus when moving a point of focusfrom an infinity side to a near side. The third lens group 3G isconstructed to have a third-a lens group 3Ga having a positiverefractive power and a third-b lens group 3Gb having a negativerefractive power, in this order from the object side, and to move onlythe third-b lens group 3Gb in a direction perpendicular to an opticalaxis, which enables a camera shake correction function to work.

The direction perpendicular to the optical axis refers to a directionwhich is perpendicular to the optical axis Z1, and a direction in whichan X-Y plane extends.

In such a manner, the basic configuration of the zoom lens 100 isdescribed above.

Further, it is desirable for the zoom lens 100 to satisfy formula (M):−2.00<f_(3a)/f_(3b)<−0.85, and more desirably, formula (M′):−1.00<f_(3a)/f_(3b)<−0.85, where f_(3a) is the focal length of thethird-a lens group 3Ga, and f_(3b) is the focal length of the third-blens group 3Gb.

Formula (M) regulates the ratio of the focal length of the third-a lensgroup 3Ga to the focal length of the third-b lens group 3Gb. If the zoomlens 100 is constructed in such a manner that the value of f_(3a)/f_(3b)is lower than the lower limit defined by formula (M), the negativerefractive power of the third-b lens group 3Gb will excessivelyincrease, so that the amount of shift of the third-b lens group 3Gb in adirection perpendicular to the optical axis, which is necessary for thecamera shake correction, will be excessively reduced. This will cause aproblem that it becomes difficult to control the camera shake correctiongroup (the third-b lens group 3Gb) against micro-vibration. If the zoomlens is constructed in such a manner that the value of f_(3a)/f_(3b)exceeds the upper limit defined by formula (M), the negative refractivepower of the third-b lens group 3Gb will be diminished and the amount ofshift of the third-b lens group 3Gb necessary for the camera shakecorrection will be excessively increased, which causes a problem that asize of the camera shake correction mechanism will become great.

It is desirable for the third-b lens group 3Gb of the zoom lens 100 tosubstantially consist of one negative lens and one positive lens. Thisenables correcting eccentric chromatic aberration which occurs at thetime of correcting the camera shake, while achieving a reduction in aweight of the third-b lens group 3Gb, thereby reducing the burden on thecamera shake correction mechanisms.

Further, it is desirable for the third-b lens group 3Gb to substantiallyconsist of two single lenses and for at least one surface to have anaspheric lens. This enables correcting eccentric comatic aberrationwhich occurs at the time of the camera shake correction, whilemaintaining a good optical performance.

The imaging apparatus 200 illustrated in FIG. 1 includes the zoom lens100, and an imaging element 210 constituted of a CCD which images anoptical image Hk (an optical image representing a subject H) formedthrough the zoom lens 100, a CMOS, or the like. An imaging surface 211of the imaging element 210 is an image formation position (an imageformation surface Mk) of the imaging lens 100.

In this case, an optical member Dg is disposed between themost-image-side lens (as indicated by the item Se in the zoom lens 100of FIG. 1) and the imaging surface 211.

Various optical members may be employed as the optical member Dgdepending on the configuration of the imaging apparatus 200 with whichthe imaging lens 100 is equipped. For example, a single or a pluralityof a member or members that correspond(s) to an imaging surfaceprotection cover glass, an infrared cut filter, an ND filter, and thelike may be provided.

Hereinafter, Examples 1 through 5 of the zoom lens of the presentinvention will be specifically described with reference to FIGS. 2A, 2B. . . 6A, 6B, 7 . . . 11 and the like.

Each zoom lens of Examples 1 through 5 satisfies the configuration ofthe zoom lens 100 and includes the following constituent elements.

Each zoom lens of Examples 1 through 5 is constituted by a first lensgroup 1G consisting of three lenses, a second lens group 2G consistingof four lenses, a third lens group 3G consisting of five lenses, afourth lens group 4G consisting of three lenses, and a fifth lens group5G consisting of two lenses.

In the first lens group 1G, a first group-first lens L1, a firstgroup-second lens L2, and a first group-third lens L3 are arranged inthis order from the object side.

Further, in the second lens group 2G, a second lens group-first lens L4,a second lens group-second lens L5, a second lens group-third lens L6,and a second lens group-fourth lens L7 are arranged in this order fromthe object side.

Further, in the third lens group 3G, a third lens group-first lens L8, athird lens group-second lens L9, a third lens group-third lens L10, athird lens group-fourth lens L11, and a third lens group-fifth lens L12are arranged in this order from the object side.

In the fourth lens group 4G, a fourth lens group-first lens L13, afourth lens group-second lens L14, and a fourth lens group-third lensL15 are arranged in this order from the object side.

Further, in the fifth lens group 5G, a fifth group-first lens L16 and afifth group-second lens L17 are arranged in this order from the objectside.

The third lens group 3G substantially consisting of five lenses asdescribed above, is constructed to have three lenses (a third-a lensgroup 3aG having positive refractive power) arranged closest to theobject side and two lenses arranged closest to the image side (a third-blens group 3bG). The third-b lens group 3bG is constructed to be movablein a direction perpendicular to an optical axis (a direction in which anX-Y plane extends), which enables a camera shake correction function towork.

In this case, the third-a lens group 3aG substantially consists of thethird group-first lens L8, the third group-second lens L9, and the thirdgroup-third lens L10, and the third-b lens group 3bG substantiallyconsists of the third group-fourth lens L11 and the third group-fifthlens L12.

An aperture stop St is disposed between the second lens group 2G and thethird lens group 3G and is designed to be moved in an optical axisdirection Z1 integrally with the third lens group 3G at the time ofvarying magnification.

Example 1

FIGS. 2A and 2B illustrate a zoom lens of Example 1. FIG. 2A is adetailed diagram illustrating the configuration of the zoom lens ofExample 1. FIG. 2B illustrates a state in which the zoom setting of thezoom lens of Example 1 is set to the wide angle end (as indicated by“WIDE” in the Figure) at the upper part and a state in which the zoomsetting thereof is set to the telephoto end (as indicated by “TELE” inthe Figure) at the bottom part. Further, arrows indicate the paths ofmovement of the lens groups, respectively when magnification is changedfrom the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 1, two lenses,i.e., a negative lens and a positive lens, are arranged in this orderfrom the object side.

Further, Table 1A to be described later shows various data related tothe zoom lens of Example 1. The upper part of Table 1A shows lens data,the middle part shows schematic specifications of the zoom lens, and thebottom part shows the focal length of each lens group.

In the lens data at the upper part of Table 1A, a surface numberrepresents the i-th (i=1, 2, 3, . . . ) lens surface or the like, andthe number sequentially increases from the most-object side toward theimage side. The aperture stop St and the optical member Dg are alsolisted in these lens data.

Radius Ri of curvature represents the radius of curvature of the i-thsurface (i=1, 2, 3, . . . ). Distance Di between surfaces (i=1, 2, 3, .. . ) represents the distance between the i-th surface and an (i+1)thsurface on the optical axis Z1. The item Ri and the item Di in the lensdata correspond to the item Si (i=1, 2, 3, . . . ) representing a lenssurface or the like.

In the column of distance Di between surfaces (i=1, 2, 3, . . . ), thereare a case in which numeral values representing the distance betweensurfaces are listed and a case in which the item Dm (m is an integralnumber). Numbers in the item Dm correspond to distances between surfaces(spatial distances), between the lens groups, and the distance betweensurfaces (spatial distance) varies depending on variable magnificationratios (zoom magnification).

Further, the item Nj represents the refractive index of a j-th (j=1, 2,3, . . . ) optical element with respect to wavelength of 587.6 nm (thed-line), and numbers sequentially increase from the object side towardthe image side. The item νj represents the Abbe number of the j-thoptical element based on the d-line.

In the lens data of Table 1A, the unit of the radius of curvature andthe distances between surfaces is mm. The radius of curvature ispositive when a convex surface faces the object side and is negativewhen a convex surface faces the image side.

The optical system as described above is generally capable ofmaintaining a predetermined performance level in any of cases where thesize of optical elements such as a lens or the like is proportionatelyincreased or decreased, and therefore zoom lenses in which the numbersof the entire lens data are proportionately increased or decreased canbe Examples related to the present invention as well.

The middle part of Table 1A represents each value of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE), i.e., distances between lens groups: D5, D13, D23, D28 and D32;f: the focal length of the entire lens system (unit mm of each value);Fno: F number; and 2ω: whole angles of view (in “°” units).

Further, the bottom part of Table 1A represents the focal length of eachgroup. In this case, f₁: the focal length of the first lens group 1G,f₂: the focal length of the second lens group 2G, f₃: the focal lengthof the third lens group 3G, f₄: the focal length of the fourth lensgroup 4G, f₅: the focal length of the fifth lens group 5G, f_(3a): thefocal length of the third-a lens group 3aG, and f_(3b): the focal lengthof the third-b lens group 3bG.

The term “the third-b group (OIS)” (OIS: Optical Image Stabilization)described in Table 1A represents being capable of achieving theperformance of the camera shake correction function by allowing thethird-b lens group 3bG to move in a direction perpendicular to theoptical axis (in a direction to which X-Y plane extends).

TABLE 1A EXAMPLE 1 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 85.75541.950 1.84661 23.9 FIRST GROUP  2 62.5697 9.119 1.49700 81.5  3−31126.9375 0.100  4 77.2118 4.299 1.61800 63.3  5 186.7731 D5  6108.0235 1.350 1.88300 40.8 SECOND  7 18.6071 8.337 GROUP  8 −55.89601.000 1.88300 40.8  9 66.9403 0.700 10 37.4987 6.589 1.84661 23.9 11−38.9747 0.362 12 −34.0881 1.000 1.75500 52.3 13 105.4506 D13 (APERTURE∞ 1.000 THIRD- STOP) 14 a GROUP 15 33.7005 3.568 1.56732 42.8 16−52.6106 0.363 17 28.4699 4.073 1.49700 81.5 18 −32.0211 0.900 1.9036631.3 19 211.4451 2.505 *20  −67.2274 1.500 1.80348 40.4 THIRD-b 2124.5327 1.041 GROUP (OIS) 22 27.2898 2.358 1.84661 23.9 23 69.3194 D23*24  49.0350 4.377 1.51560 63.1 FOURTH *25  −43.0727 0.169 GROUP 2646.1728 1.000 1.84661 23.9 27 22.9572 6.496 1.51680 64.2 28 −48.8859 D28*29  85.0541 1.500 1.80348 40.4 FIFTH *30  20.5630 0.099 GROUP 3119.5078 2.277 1.92286 20.9 32 25.9096 D32 33 ∞ 3.700 1.51680 64.2 Dg 34∞ WIDE MID TELE D5 0.950 32.298 66.596 D13 42.834 15.932 3.617 D2312.578 6.213 3.622 D28 2.153 3.937 1.901 D32 35.505 66.444 82.661 f18.384 67.549 248.190 Fno 3.60 5.48 6.49 2ω [°] 76.61 22.49 6.22 f₁111.303 f₂ −17.195 f₃ 89.768 f₄ 28.523 f₅ −59.029 f_(3a) 33.607 f_(3b)(OIS) −39.462

Table 1B shows aspheric coefficients of aspheric surfaces of the zoomlens of Example 1. In the lens data of Table 1A, the mark “*” attachedto a surface number indicates that a surface represented by the surfacenumber is an aspheric surface. Further, Table 1B shows the asphericcoefficients of aspheric surfaces corresponding to these surfacenumbers.

The aspheric coefficients represented in Table 1B are prepared to defineaspheric shapes by being applied in the following aspheric equation.

Z=C·h ²/{1+(1−K·C ² ·h ²)^(1/2) }+ΣAn·h ^(n)  [Aspheric Equation 1]

whereZ: the depth of an aspheric surface (mm)h: the distance from the optical axis to a lens surface (height) (mm)K: aspheric coefficients representing quadric surfaceC: paraxial curvature=1/R (R: paraxial curvature radius)An: n-dimensional (n is an integer not less than three) asphericcoefficient

TABLE 1B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *24 *25 *29 *30 K1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 A3−6.660863E−06 2.113073E−05 1.195308E−05 6.668667E−07 1.051388E−05 A41.068409E−05 −1.787018E−05 9.213718E−07 −1.182857E−07 −3.423284E−06 A5−6.114474E−07 −3.133994E−07 2.202715E−08 −9.254225E−09 7.184053E−07 A63.008719E−08 1.883512E−07 −6.561077E−10 −4.950193E−10 −1.065630E−08 A72.785752E−09 −2.494012E−08 −1.302087E−10 −1.901654E−11 −4.565539E−09 A8−7.187710E−11 1.247161E−09 −1.087276E−11 −1.551834E−13 −1.629647E−11 A9−1.749371E−11 9.724427E−14 −6.432469E−13 7.118640E−14 4.500121E−11 A105.214071E−13 −1.350450E−12 −2.148723E−14 1.063682E−14 −1.679259E−12 A11−9.928876E−17 9.672666E−16 −1.039705E−15 1.136476E−15 1.043516E−15 A12−1.891767E−16 1.223378E−17 −3.166091E−17 1.069028E−16 7.735059E−17 A13−6.521684E−17 −4.164422E−18 1.294460E−18 9.376248E−18 6.733229E−18 A14−1.390141E−17 −7.285136E−19 3.747765E−19 7.834346E−19 6.654046E−19 A15−1.714540E−18 7.231878E−20 8.216610E−20 2.319643E−19 2.466336E−19 A16−2.682522E−19 4.235680E−21 9.394894E−21 1.747560E−20 2.657868E−20

FIG. 7 is a diagram showing spherical aberration, astigmatism,distortion, and lateral chromatic aberration at each of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE). Further, aberrations of each light beam of the d-line and theg-line are shown in the Figure. The diagram of astigmatism representsaberrations with respect to sagittal image surfaces and tangential imagesurfaces.

As shown in FIG. 7, diagrams indicated by the symbols Wa, Ma, and Tarepresent spherical aberration, diagrams indicated by the symbols Wb,Mb, and Tb represent astigmatism, diagrams indicated by the symbols Wc,Mc, and Tc represent distortion, and diagrams indicated by the symbolsWd, Md, and Td represent lateral chromatic aberration.

Table 6 as shown at the end of the description of the Examplesrepresents values (values evaluated from mathematical expression offormula (M)) of formula (M) for Examples 1 through 5, individually. Themathematical expression of each formula can be evaluated from variousdata and the like with respect to the zoom lenses in Tables 1A through5A.

As can be seen from the above lens data and the like, the zoom lens ofExample 1 has a high variable ratio, and yet is compact and capable ofhigh performance.

FIGS. 2A and 2B illustrating a configuration of the zoom lens of Example1, FIG. 7 illustrating aberrations of the zoom lens, Tables 1A & 1Brepresenting the lens data and the like of the zoom lens, and Table 6representing the values of each mathematical expression of formula (M)are read in the same manner as in Examples through 5 to be describedlater, and therefore detailed descriptions thereof will be omitted.

Example 2

FIGS. 3A and 3B show a zoom lens of Example 2. FIG. 3A is a diagramillustrating the specific configuration of the zoom lens of Example 2.FIG. 3B is related to the zoom lens of Example 2, and illustrates astate in which the zoom setting is set to a wide angle end (as indicatedby “WIDE” in the Figure) at the upper part and a state in which the zoomsetting thereof is set to a telephoto end (as indicated by “TELE” in theFigure) at the bottom part. Further, arrows indicate the paths ofmovement of the lens groups, respectively when magnification is changedfrom the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 2, two lenses,i.e., a positive lens and a negative lens, are arranged in this orderfrom the object side.

Further, Table 2A shows various data related to the zoom lens of Example2. The upper part of Table 2A shows lens data, the middle part showsschematic specifications of the zoom lens, and the bottom part shows thefocal length of each lens group.

TABLE 2A EXAMPLE 2 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTUER  1 85.22922.520 1.84661 23.9 FIRST GROUP  2 61.7335 9.054 1.49700 81.5  3−1963.5475 0.100  4 66.8404 4.168 1.60300 65.4  5 147.8987 D5  6 88.04381.400 1.88300 40.8 SECOND  7 18.3402 8.245 GROUP  8 −50.9539 1.0501.83481 42.7  9 63.5833 1.045 10 37.5330 6.423 1.84661 23.9 11 −37.53300.405 12 −32.6020 1.050 1.77250 49.6 13 97.2521 D13 (APERTURE ∞ 1.000THIRD-a STOP) 14 GROUP 15 33.0761 3.238 1.54814 45.8 16 −58.1129 0.21817 29.9896 4.828 1.49700 81.5 18 −29.9896 0.900 1.85026 32.3 19 200.12564.148 *20  −64.3421 1.500 1.80168 40.7 THIRD-b *21  24.7941 0.835 GROUP(OIS) 22 27.9314 2.293 1.84661 23.9 23 67.4658 D23 *24  52.0924 4.6031.51530 62.8 FOURTH *25  −41.7940 0.118 GROUP 26 48.9063 1.050 1.7552027.5 27 23.5612 5.631 1.48749 70.2 28 −52.7318 D28 29 −77.6900 2.3621.80518 25.4 FIFTH 30 −34.1433 1.323 GROUP *31  −38.3946 1.500 1.8016840.7 *32  175.1091 D32 33 ∞ 5.200 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D50.900 34.251 61.985 D13 43.622 17.798 3.965 D23 10.401 5.906 3.496 D283.770 5.315 1.700 D32 33.109 60.979 85.617 f 18.388 67.562 248.238 Fno3.60 5.18 6.47 2ω [°] 76.59 22.60 6.27 f₁ 105.536 f₂ −16.856 f₃ 97.458f₄ 29.520 f₅ −84.482 f_(3a) 35.192 f_(3b) (OIS) −37.423

Table 2B shows aspheric coefficients of aspheric surfaces of the zoomlens of Example 2.

TABLE 2B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *21 *24 *25 *31*32 K  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00 1.000000E+00  1.000000E+00 A3 −6.214685E−06  1.210237E−06  2.670345E−05 1.418960E−05 −6.078072E−06  7.219238E−07 A4  1.178008E−05 −2.059917E−07−1.699876E−05  3.117539E−07 −8.397924E−08 −1.310513E−07 A5 −5.734545E−07−7.148778E−09 −2.869234E−07  2.819776E−09 −3.195286E−07 −3.857289E−09 A6 2.988894E−08  1.380535E−10  1.883256E−07 −7.772038E−10 −4.462125E−09−5.848393E−10 A7  2.617898E−09  2.608762E−11 −2.502808E−08 −9.142656E−11 2.561994E−09 −7.783658E−11 A8 −9.134118E−11  1.435216E−13  1.237420E−09−6.908198E−12  7.007254E−11 −7.925124E−12 A9 −1.920589E−11 −3.192440E−13−6.986446E−13 −4.003267E−13 −2.680817E−11 −7.016044E−13 A10 3.923019E−13 −5.843137E−14 −1.406596E−12 −1.483360E−14  9.907504E−13−5.825802E−14 A11 −7.929852E−15 −7.084585E−15 −2.653633E−15−1.835598E−15 −9.622458E−15 −4.777413E−15 A12 −6.308512E−16−6.646965E−16 −2.176749E−16 −2.125550E−16 −9.379487E−16 −4.039401E−16A13 −5.271484E−17 −4.473916E−17 −2.116950E−17 −2.258551E−17−8.488742E−17 −3.628087E−17 A14 −2.605892E−18 −6.306065E−19−2.497013E−18 −2.231667E−18 −7.080190E−18 −3.496352E−18 A15 1.622770E−18  4.767090E−19 −2.199383E−19 −3.898770E−19 −6.276121E−19−8.095367E−19 A16  3.760341E−19  1.155446E−19 −2.569275E−20−4.124631E−20 −3.345415E−20 −9.331008E−20

FIG. 8 is a diagram showing spherical aberration, astigmatism,distortion, and lateral chromatic aberration at each of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE) of the zoom lens of Example 2.

Example 3

FIGS. 4A and 4B show a zoom lens of Example 3. FIG. 4A is a diagramillustrating the specific configuration of the zoom lens of Example 3.FIG. 4B is related to the zoom lens of Example 3, and illustrates astate in which the zoom setting is set to a wide angle end (as indicatedby “WIDE” in the Figure) at the upper part and a state in which the zoomsetting thereof is set to a telephoto end (as indicated by “TELE” in theFigure) at the bottom part. Further, arrows indicate the paths ofmovement of the lens groups, respectively when magnification is changedfrom the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 3, two lenses,i.e., a positive lens and a negative lens, are arranged in this orderfrom the object side.

Further, Table 3A shows various data related to the zoom lens of Example3. The upper part of Table 3A shows lens data, the middle part showsschematic specifications of the zoom lens, and the bottom part shows thefocal length of each lens group.

TABLE 3A EXAMPLE 3 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 86.12271.650 1.84661 23.9 FIRST GROUP  2 62.0701 9.553 1.49700 81.5  3−4250.8858 0.200  4 69.0201 5.134 1.61800 63.3  5 173.7706 D5  6143.9195 1.250 1.88300 40.8 SECOND  7 17.9097 8.359 GROUP *8 −54.18750.200 1.52771 41.8  9 −52.5929 1.000 1.80400 46.6 10 61.2864 1.229 1138.6886 5.875 1.84661 23.9 12 −38.4723 1.010 1.80400 46.6 13 99.9343 D13(APERTURE ∞ 1.000 THIRD-a STOP) 14 GROUP 15 32.7747 3.500 1.54814 45.816 −52.1190 1.172 17 28.6007 4.608 1.49700 81.5 18 −31.7142 1.0001.90366 31.3 19 247.9630 2.532 *20  −62.9067 1.500 1.80348 40.4 THIRD-b21 24.4096 1.000 GROUP (OIS) 22 26.9299 2.518 1.84661 23.9 23 65.6490D23 *24  49.2954 4.978 1.51560 63.1 FOURTH *25  −44.8007 1.459 GROUP 2647.4064 0.900 1.84661 23.9 27 23.0755 6.115 1.51680 64.2 28 −45.9160 D2829 −225.5534 2.848 1.84661 23.9 FIFTH 30 −35.6067 0.500 GROUP *31 −39.1114 1.500 1.80348 40.4 *32  54.4009 D32 33 ∞ 3.700 1.51680 64.2 Dg34 ∞ WIDE MID TELE D5 0.999 31.879 61.061 D13 42.746 17.373 4.203 D2311.516 5.965 3.499 D28 1.951 3.394 1.885 D32 35.490 64.031 78.012 f18.382 64.988 229.769 Fno 3.62 5.22 6.08 2ω [°] 76.61 23.33 6.73 f₁103.033 f₂ −16.513 f₃ 87.566 f₄ 29.127 f₅ −66.647 f_(3a) 33.407 f_(3b)(OIS) −37.492

Table 3B shows aspheric coefficients of aspheric surfaces of the zoomlens of Example 3.

TABLE 3B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *8 *20 *24 *25 *31 *32K 1.464546E+00  1.000000E+00 1.000000E+00  1.000000E+00  1.000000E+00 1.000000E+00 A3 0.000000E+00 −6.784837E−06 2.196427E−05  1.195660E−05−1.149323E−05 −1.143922E−06 A4 2.212057E−06  1.073941E−05 −1.784348E−05  8.656127E−07 −3.692099E−07  8.049956E−10 A5 0.000000E+00 −6.120021E−07−3.189917E−07   2.476411E−08 −3.237427E−07 −3.487018E−10 A6−8.509320E−09   2.983909E−08 1.875408E−07 −4.076491E−11 −4.237706E−09−1.612101E−10 A7 0.000000E+00  2.765409E−09 −2.501350E−08  −6.934857E−11 2.612386E−09 −2.141371E−11 A8 1.827402E−11 −7.300686E−11 1.241716E−09−6.189639E−12  7.725014E−11 −1.924803E−12 A9 0.000000E+00 −1.754200E−11−2.534825E−13  −3.333725E−13 −2.592973E−11 −1.269553E−13 A10−1.356278E−13   5.200665E−13 −1.369651E−12  −3.716054E−15  1.087591E−12−4.597426E−15 A11  4.577131E−17 2.121105E−16 −2.243534E−16  2.093262E−16 3.219858E−16 A12 −1.519797E−16 1.643937E−17 −1.434839E−17 −8.269620E−18 9.836844E−17 A13 −5.440776E−17 1.428068E−18 −9.633478E−19 −2.966776E−18 1.494300E−17 A14 −1.137249E−17 1.494776E−19 −8.031938E−20 −4.355006E−19 1.856954E−18

FIG. 9 is a diagram showing spherical aberration, astigmatism,distortion, and lateral chromatic aberration at each of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE) of the zoom lens of Example 3.

Example 4

FIGS. 5A and 5B show a zoom lens of Example 4. FIG. 5A illustrates thespecific configuration of the zoom lens of Example 4. FIG. 5B is relatedto the zoom lens of Example 4, and illustrates a state in which the zoomsetting is set to a wide angle end (as indicated by “WIDE” in theFigure) at the upper part and a state in which the zoom setting thereofis set to a telephoto end (as indicated by “TELE” in the Figure) at thebottom part. Further, arrows indicate the paths of movement of the lensgroups, respectively when magnification is changed from the wide angleend to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 4, two lenses,i.e., a positive lens and a negative lens, are arranged in this orderfrom the object side.

Further, Table 4A shows various data related to the zoom lens of Example4. The upper part of Table 4A shows lens data, the middle part showsschematic specifications of the zoom lens, and the bottom part shows thefocal length of each lens group.

TABLE 4A EXAMPLE 4 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 84.94631.950 1.84661 23.9 FIRST GROUP  2 62.2446 8.693 1.49700 81.5  3 ∞ 0.100 4 68.3452 4.363 1.60300 65.4  5 153.8323 D5  6 89.2120 1.350 1.8830040.8 SECOND  7 18.2963 8.233 GROUP  8 −58.1632 1.000 1.88300 40.8  967.7426 0.948 10 37.5173 6.506 1.84661 23.9 11 −38.5206 0.408 12−33.7911 1.000 1.77250 49.6 13 99.4178 D13 (APERTURE ∞ 1.000 THIRD-aSTOP) 14 GROUP 15 33.6716 3.293 1.51742 52.4 16 −58.3051 0.100 1728.2935 4.126 1.49700 81.5 18 −31.9738 0.900 1.83400 37.2 19 127.34052.569 20 −68.3981 2.272 1.84661 23.9 THIRD-b 21 −26.8082 0.886 GROUP(OIS) 22 −24.8406 1.500 1.80348 40.4 *23  62.6811 D23 *24  49.8918 4.4521.51560 63.1 FOURTH *25  −42.8733 0.100 GROUP 26 53.2553 1.000 1.8051825.4 27 23.3404 5.973 1.51823 58.9 28 −46.7603 D28 29 −81.9572 2.3571.80518 25.4 FIFTH 30 −34.7267 1.493 GROUP *31  −38.2183 1.500 1.8034840.4 *32  179.9979 D33 33 ∞ 4.900 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D50.900 33.799 63.266 D13 44.713 17.634 3.566 D23 11.185 6.816 4.357 D283.245 4.848 1.970 D32 34.996 63.954 86.941 f 18.366 67.481 247.941 Fno3.60 5.26 6.55 2ω [°] 76.64 22.68 6.28 f₁ 107.872 f₂ −17.446 f₃ 116.489f₄ 29.082 f₅ −85.750 f_(3a) 37.832 f_(3b) (OIS) −39.192

Table 4B shows aspheric coefficients of aspheric surfaces of the zoomlens of Example 4.

TABLE 4B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *23 *24 *25 *31 *32 K1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 A31.288744E−05 2.647809E−05 1.085607E−05 −7.403052E−06 −1.039624E−07 A4−1.078292E−05 −1.725827E−05 4.339778E−07 −1.719981E−07 −1.241135E−07 A56.382901E−07 −2.955264E−07 7.445503E−09 −3.195104E−07 −6.411543E−09 A6−2.635804E−08 1.884390E−07 −7.830304E−10 −4.172605E−09 −7.019777E−10 A7−2.463874E−09 −2.498717E−08 −1.006144E−10 2.599459E−09 −6.791905E−11 A89.303492E−11 1.241227E−09 −7.050127E−12 7.428064E−11 −5.579190E−12 A91.836592E−11 −4.496962E−13 −3.044782E−13 −2.634935E−11 −4.226272E−13 A10−5.521081E−13 −1.394620E−12 3.515842E−15 1.038713E−12 −3.175412E−14 A11−1.312550E−14 −2.307759E−15 5.035691E−16 −4.914561E−15 −2.523663E−15 A12−1.649716E−15 −2.136162E−16 3.668331E−17 −5.118335E−16 −2.219919E−16 A13−1.438455E−16 −1.859723E−17 1.097923E−18 −5.040249E−17 −2.163300E−17 A14−6.585779E−18 −1.568050E−18 −1.859078E−19 −4.774574E−18 −2.263951E−18A15 −4.147342E−19 −2.121945E−20 −2.309610E−19 −5.390733E−19−6.968129E−19 A16 1.147946E−19 8.062655E−21 −3.078231E−20 −4.101269E−20−8.198580E−20

FIG. 10 is a diagram showing spherical aberration, astigmatism,distortion, and lateral chromatic aberration at each of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE) of the zoom lens of Example 4.

Example 5

FIGS. 6A and 6B show a zoom lens of Example 5. FIG. 6A illustrates thespecific configuration of the zoom lens of Example 5. FIG. 6B is relatedto the zoom lens of Example 5, and illustrates a state in which the zoomsetting is set to a wide angle end (as indicated by “WIDE” in theFigure) at the upper part and a state in which the zoom setting thereofis set to a telephoto end (as indicated by “TELE” in the Figure) at thebottom part. Further, arrows indicate the paths of movement of the lensgroups, respectively when magnification is changed from the wide angleend to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 5, two lenses,i.e., a positive lens and a negative lens, are arranged in this orderfrom the object side.

Further, Table 5A shows various data related to the zoom lens of Example5. The upper part of Table 5A shows lens data, the middle part showsschematic specifications of the zoom lens, and the bottom part shows thefocal length of each lens group.

TABLE 5A EXAMPLE 5 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 85.29922.520 1.84661 23.9 FIRST GROUP  2 61.8500 9.114 1.49700 81.5  3−2375.7864 0.100  4 66.8941 4.269 1.60300 65.4  5 146.5034 D5  6 87.89981.400 1.88300 40.8 SECOND  7 18.3570 8.315 GROUP  8 −51.0001 1.0501.83481 42.7  9 63.6139 0.815 10 37.4113 6.407 1.84666 23.8 11 −37.41130.388 12 −32.5753 1.050 1.77250 49.6 13 98.4906 D13 (APERTURE ∞ 1.100THIRD-a STOP) 14 GROUP 15 34.2381 3.329 1.54814 45.8 16 −60.1143 0.93717 27.0475 4.232 1.49700 81.5 18 −33.1140 0.900 1.85026 32.3 19 163.64203.836 *20  −63.3026 1.500 1.80168 40.7 THIRD-b *21  24.7365 0.864 GROUP(OIS) 22 28.0299 2.277 1.84666 23.8 23 66.7227 D23 *24  52.7776 4.6751.51530 62.8 FOURTH *25  −42.2885 0.105 GROUP 26 48.3349 1.050 1.7552027.5 27 23.5950 5.625 1.48749 70.2 28 −52.9320 D28 29 −77.2285 2.3601.80518 25.4 FIFTH 30 −34.0317 1.053 GROUP *31  −38.4236 1.500 1.8016840.7 *32  175.0302 D32 33 ∞ 5.200 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D50.900 36.423 62.766 D13 43.473 17.944 3.610 D23 10.708 6.338 3.715 D283.842 5.548 1.698 D32 33.106 58.073 84.416 f 18.389 67.564 248.247 Fno3.62 5.02 6.39 2ω [°] 76.66 22.61 6.27 f₁ 106.443 f₂ −16.902 f₃ 94.599f₄ 29.607 f₅ −84.036 f_(3a) 34.301 f_(3b) (OIS) −36.710

Table 5B shows aspheric coefficients of aspheric surfaces of the zoomlens of Example 5.

TABLE 5B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *21 *24 *25 *31*32 K  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00 1.000000E+00  1.000000E+00 A3 −6.165192E−06  1.136414E−06  2.646484E−05 1.455922E−05 −5.608010E−06  3.111280E−07 A4  1.180918E−05 −2.391292E−07−1.700884E−05  3.247792E−07 −6.243737E−08 −1.509737E−07 A5 −5.712797E−07−9.755106E−09 −2.879359E−07  3.790736E−09 −3.186333E−07 −4800208E−09 A6 3.004106E−08 −5.784070E−11  1.882504E−07 −7.189621E−10 −4.429101E−09−6.392048E−10 A7  2.628840E−09  1.065292E−11 −2.503214E−08 −8.915027E−11 2.562357E−09 −8.139704E−11 A8 −9.058174E−11 −1.062813E−12  1.237303E−09−6.929168E−12  6.993044E−11 −8.143708E−12 A9 −1.916284E−11 −4.032273E−13−6.914544E−13 −4.165896E−13 −2.683328E−11 −7.108067E−13 A10 3.931210E−13 −6.248737E−14 −1.404954E−12 −1.706208E−14  9.877237E−13−5.801155E−14 A11 −8.205763E−15 −6.993822E−15 −2.471879E−15−2.065580E−15 −9.923479E−15 −4.652135E−15 A12 −6.918798E−16−6.032048E−16 −2.028307E−16 −2.332995E−16 −9.630020E−16 −3.833882E−16A13 −6.145538E−17 −3.361798E−17 −2.032344E−17 −2.430529E−17−8.645582E−17 −3.363706E−17 A14 −3.613976E−18  8.786762E−19−2.491248E−18 −2.366453E−18 −7.105990E−18 −3.193681E−18 A15 1.528779E−18  6.479148E−19 −2.276198E−19 −4.001489E−19 −6.139199E−19−7.773001E−19 A16  3.702179E−19  1.315589E−19 −2.724708E−20−4.204166E−20 −3.018856E−20 −9.005424E−20

FIG. 11 is a diagram showing spherical aberration, astigmatism,distortion, and lateral chromatic aberration at each of a wide angle end(WIDE), the middle of varying magnification (MID), and a telephoto end(TELE) of the zoom lens of Example 5.

The zoom lens of Example 5, which is constructed in such a manner, canhave a high variable magnification ratio, and yet be compact and capableof high performance.

TABLE 6 EXAM- EXAM- EXAM- EXAM- PLE 1 PLE 2 PLE 3 PLE 4 EXAMPLE 5FORMULA (M) −0.852 −0.940 −0.891 −0.965 −0.934

The above zoom lens may have the following configuration. All of thezoom lenses of the above Examples 1 through 5 are assumed to have theconfiguration as shown below.

It should be noted that in the zoom lens of the present invention, thefifth lens group 5G has at least one aspheric surface, and that it isdesirable for the zoom lens to satisfy formula (A): 10<ν_(5n)−ν_(5p)<30and formula (B): 1.77<N₅, at the same time, and it is more desirable forthe zoom lens to satisfy formula (A′): 12<ν_(5n)−ν_(5p)<25 and/orformula (B′): 1.79<N_(5n).

In this case, ν_(5n) is an average value of the Abbe number (based onthe d-line) of each lens having negative refractive power, whichconstitute the fifth lens group 5G; ν_(5p) is an average value of theAbbe number (based on the d-line) of each lens having positiverefractive power, which constitute the fifth lens group 5G; and N_(5n)is an average value of the refractive index (with respect to the d-line)of each lens having negative refractive power, which constitute thefifth lens group 5G.

As described above, if the fifth lens group has at least one asphericsurface, performance variations can be favorably suppressed at the timeof focusing.

Formula (A) regulates the Abbe number with respect to the d-line of anegative lens and a positive lens that constitute the fifth lens group5G. If the zoom lens is constructed in such a manner that the value ofν_(5n)−ν_(5p) is lower than the lower limit defined by formula (A),correction for chromatic aberration within the fifth lens group 5G willbe insufficient, and chromatic aberration will become a problem at thetime of focal shift. Meanwhile, if the zoom lens is constructed in sucha manner that the value of ν_(5n)−ν_(5p) exceeds the upper limit definedby formula (A), correction for chromatic aberration within the fifthlens group 5G is sufficient, but the refractive index of the negativelens will be forced to be small. This will cause a problem that thecurvature of image field of a peripheral image will become large.

Formula (B) regulates the refractive index with respect to the d-line ofa negative lens within the fifth lens group 5G. If the zoom lens 100 isconstructed in such a manner that the value of N_(5n) is lower than thelower limit defined by formula (B), a refractive index of the negativelens within the fifth lens group 5G becomes too small, which will causea problem that the curvature of image field of a peripheral image willbecome more likely to occur.

Further, it is desirable for the zoom lens to satisfy formula (C):−0.6<1−β_(5T) ²<−2.5, and more desirably, formula (C′): −5.5<1−β_(5T)²<−2.9.

β_(5T) is an image formation magnification of the fifth lens group 5Gwhen focusing on infinity at the telephoto end.

Formula (C) regulates the sensitivity to image shift with respect to afocal shift at the time of focusing on infinity at the telephoto end inthe fifth lens group 5G. If the zoom lens 100 is constructed in such amanner that the value of 1−β_(5T) ² is lower than the lower limitdefined by formula (C), the sensitivity to the image shift with respectto the focal shift of the fifth lens group 5G at the telephoto end willbe excessively increased, which will cause the amount of amplitude shiftof the fifth lens group 5G for finding the best point of focus to beexcessively reduced. As a result, problems such that it will becomedifficult to perform focus control, for example, the focal shift of thefifth lens group 5G becoming suspended, will arise. If the zoom lens 100is constructed in such a manner that the value of 1−β_(5T) ² exceeds theupper limit defined by formula (C), the sensitivity of the image shiftwith respect to the focal shift of the fifth lens group 5G will beacceptable at the telephoto end, but the sensitivity at the wide angleend will be excessively reduced. This will cause the amount of amplitudeshift of the fifth lens group 5G for finding the best point of focus tobe excessively increased. As a result, for example, problems, thatabnormal noises are made by the focusing mechanism at the time of thefocus shift, will arise.

The fifth lens group 5G comprises a positive lens and a negative lens,and it is desirable to arrange the positive lens and the negative lensin this order from the object side. This enables the fifth lens group 5Gto be constituted by the requisite minimum number of lenses which cansuppress performance variations at the time of focusing, therebyreducing the burden on the focusing mechanism and achieving high-speedfocus. Further, the arrangement of the positive lens and the negativelens in this order from the object side facilitates divergence ofreflection on each lens surface for a light beam which is reflected onthe imaging surface of the imaging element and which returns to thefifth lens group 5G because more convex surfaces of the lensesconstituting the fifth lens group 5G face toward the image side. Thisreduces the generation of eye-catching ghost images.

That is, it is desirable for the above zoom lens to satisfy formula (D):0.10<f_(w)/f₁<0.25; and more desirably, formula (D′):0.15<f_(w)/f₁<0.20, where f_(w) is the focal length of the entire lenssystem at a wide angle end and f₁ is the focal length of the first lensgroup 1G.

Formula (D) regulates the ratio of the focal length of the entire lenssystem at a wide angle end to the focal length of the first lens group1G. If the zoom lens is constructed in such a manner that the value off_(w)/f₁ is less than the lower limit defined by formula (D), the focallength of the first lens group 1G becomes too large, which causes aproblem that the outer diameters of the lenses of the first lens group1G and the total length of the optical system will become great at thetelephoto end. If the zoom lens is constructed in such a manner that thevalue of f_(w)/f₁ exceeds the upper limit defined by formula (D),positive refractive power of the first lens group 1G becomes too strong,which will cause a problem that it becomes difficult to maintain opticalperformance at the telephoto end.

Further, it is desirable for the zoom lens to satisfy formula (F):−1.5<f_(w)/f₂<−0.5, and more desirably, formula (F′):−1.2<f_(w)/f₂<−1.0, where F₂ is the focal length of a second lens group2G.

Formula (F) regulates the ratio of the focal length of the entire lenssystem at a wide angle end to the focal length of the second lens group2G. If the zoom lens is constructed in such a manner that the value off_(w)/f₂ is lower than the lower limit defined by formula (F), negativerefractive power of the second lens group 2G will be excessivelyincreased, which will cause a problem that the curvature of image fieldof a peripheral image will become large. Further, a problem ofdifficulties in maintaining optical performance when magnification isvaried will also occur. If the zoom lens is constructed in such a mannerthat the value of f_(w)/f₂ exceeds the upper limit defined by formula(F), negative refractive power of the second lens group 2G will beexcessively reduced, which will increase the amount of shift of thefirst lens group 1G when magnification is varied. This will cause aproblem that the outer diameters of the lenses of the first lens group1G and the total length of the optical system will become great at thetelephoto end.

Further, it is desirable for the zoom lens to satisfy formula (H):0.10<f_(w)/f₃<0.50, and more desirably, formula (H′):0.15<f_(w)/f₃<0.30, where f₃ is the focal length of a third lens group3G.

Formula (H) regulates the ratio of the focal length of the entire lenssystem at a wide angle end to the focal length of the third lens group3G. If the zoom lens is constructed in such a manner that the value off_(w)/f₃ is lower than the lower limit defined by formula (H), positiverefractive power of the third lens group 3G will be excessively reduced,which will increase the amount of shift of the third lens group 3G whenmagnification is varied. This causes a problem that the total length ofthe optical system grows to a large size. If the zoom lens isconstructed in such a manner that the value of f_(w)/f₃ exceeds theupper limit defined by formula (H), positive refractive power of thethird lens group 3G will be excessively increased. This will cause aproblem of difficulties in maintaining optical performance whenmagnification is varied.

Further, it is desirable for the zoom lens to satisfy formula (J):0.50<f_(w)/f₄<0.65 and formula (K): −0.32<f_(w)/f₅<−0.15 at the sametime, and more desirably, formula (J′): 0.60<f_(w)/f₄<0.65 and/orformula (K′): −0.32<f_(w)/f₅<−0.20, where f₄ is the focal length of thefourth lens group 4G and f₅ is the focal length of the fifth lens group5G.

Formula (J) regulates the ratio of the focal length of the entire lenssystem at a wide angle end to the focal length of the fourth lens group4G. If the zoom lens is constructed in such a manner that the value off_(w)/f₄ is lower than the lower limit defined by formula (J), positiverefractive power of the fourth lens group 4G will be excessivelyreduced, which will increase the amount of shift of the fourth lensgroup 4G when magnification is varied. This will cause a problem thatthe total length of the optical system will become great. If the zoomlens is constructed in such a manner that the value of f_(w)/f₄ exceedsthe upper limit defined by formula (J), positive refractive power of thefourth lens group 4G will be excessively increased. This will cause aproblem of difficulties in maintaining optical performance whenmagnification is varied.

Formula (K) regulates the ratio of the focal length of the entire lenssystem at a wide angle end to the focal length of the fifth lens group5G. If the zoom lens is constructed in such a manner that the value off_(w)/f₅ is lower than the lower limit defined by formula (K), negativerefractive power of the fifth lens group 5G will be excessivelyincreased, which will causes a problem that the back focus length willbecomes longer and the entire length of the optical system will becomegreat. If the zoom lens is constructed in such a manner that the valueof f_(w)/f₅ exceeds the upper limit defined by formula (K), negativerefractive power of the fifth lens group 5G will be excessively reduced,which will diminish the back focus length. This will cause a problemthat spaces for a mirror of a single-lens reflex camera, a filter, andthe like cannot be secured, for example. In addition, the amount ofshift of the fifth lens group 5G will be increased at the time of focus,and further the outer diameters of the lenses of the fifth lens group 5Gwill become great. This increases the burden on the focusing mechanismso that it will become difficult to achieve high-speed focus, forexample.

The present invention is not limited to the embodiments and the examplesdescribed above, and various modifications are possible. For example,values, such as the radius of curvature of each lens element, distancesbetween surfaces, and refractive indices, are not limited to the valuesin the numerical examples shown in the Tables, but may be other values.

What is claimed is:
 1. A zoom lens, substantially consisting of: a firstlens group having positive refractive power; a second lens group havingnegative refractive power; a third lens group having positive refractivepower; a fourth lens group having positive refractive power; and a fifthlens group having negative refractive power, which are arranged in thisorder from an object side of the zoom lens, wherein when varyingmagnification from a wide angle end to a telephoto end, the distancebetween the first lens group and the second lens group is consistentlyincreased, the distance between the second lens group and the third lensgroup is consistently decreased, the distance between the third lensgroup and the fourth lens group is consistently decreased, and thedistance between the fourth lens group and the fifth lens group ischanged, while all of the lens groups are moved with respect to an imageformation position, wherein when moving a point of focus from aninfinity side to a near side to achieve focus, only the fifth lens groupis moved to the image side, wherein the third lens group comprises athird-a lens group having positive refractive power and a third-b lensgroup having negative refractive group, which are arranged in this orderfrom the object side, only the third-b lens group is moved in adirection perpendicular to the optical axis to achieve camera shakecorrection, and the following formula (M) is satisfied:−2.00<f _(3a) /f _(3b)<−0.85  (M), where f_(3a): the focal length of thethird-a lens group, and f_(3b): the focal length of the third-b lensgroup.
 2. The zoom lens as defined in claim 1, wherein the followingformula (M′) is satisfied:−1.00<f _(3a) /f _(3b)<−0.85  (M′) f_(3a): the focal length of thethird-a lens group, and f_(3b): the focal length of the third-b lensgroup.
 3. The zoom lens as defined in claim 1, wherein the third-b lensgroup comprises one negative lens and one positive lens.
 4. The zoomlens as defined in claim 1, wherein the third-b lens group comprises twosingle lenses and has at least one aspheric surface.
 5. The zoom lens asdefined in claim 2, wherein the third-b lens group comprises onenegative lens and one positive lens.
 6. The zoom lens as defined inclaim 2, wherein the third-b lens group comprises two single lenses andhas at least one aspheric surface.
 7. An imaging apparatus comprising:the zoom lens as defined in claim 1.